The long term objectives of this research plan is to define how interactions during post-natal development between pathways within the auditory system determine the structure and function of the auditory system. While it is known that afferent neurons play a critical role in the development and maintenance of targeted cells in the auditory system, the emphasis in this research is the interactions during development between pathways that convey information from each ear. How will pathways conveying information from one ear develop in an animal deprived from birth of sensory information of the other ear? The focus of the present proposal is the localization and definition of the interactions between pathways that occur during the post-natal development of the lower brainstem auditory system. The projections from the cochlear nuclear complex to the component nuclei of the superior olivary complex and nuclei of the lateral lemniscus bilaterally will be examined in control gerbils and in adult gerbils that had been subjected at two days of age to the ablation of one cochlea. These projections will be compared by injecting anterograde tracers into the cochlear nuclear complex on the non-operated side in experimental animals and into one cochlear nucleus of control animals. Secondly, functional differences between the brainstem auditory system of animals that had developed with one or with both cochleas will be studied by analyzing responses of single neurons in those nuclei. Responses to stimulation of the non-operated ear in a neonatally ablated animal will be compared with responses to monaural stimulation in control animals. This research is related to the consequences of perinatal loss of hearing in humans, as often happens, for example, in cases of maternal rubella. Understanding the anatomical and physiological consequences of the neonatal loss of the cochlea in the gerbil shold provide a greater understanding of the clinical situation in humans.